The invention generally relates to techniques for preventing heart arrhythmias and in particular to techniques for preventing ventricular arrhythmias of the type that can result in Sudden Cardiac Death.
Sudden Cardiac Death (xe2x80x9cSCDxe2x80x9d) claims about 300,000 lives a year in the United States alone. In most cases, the direct cause of SCD is a ventricular tachycardia (xe2x80x9cVTxe2x80x9d) which triggers a ventricular fibrillation (xe2x80x9cVFxe2x80x9d). VT and VF are different types of ventricular arrhythmias. VT is an abnormally fast ventricular heart rhythm which is, by itself, typically not fatal. VF is a chaotic ventricular heart rhythm which produces little or no net blood flow from the heart, such that there is little or no net blood flow to the brain and other organs. VF, if not terminated, results in death. In most cases of SCD, the victim has a previous myocardial infarction (xe2x80x9cMIxe2x80x9d), i.e. the patient had a previous heart attack caused by blockage of a portion of the coronary artery which supplies blood to the heart muscle. As a result of the blockage, a portion of the heart muscle does not receive blood and therefore becomes scarred and diseased. The scarred and diseased portion of the heart is referred to as the MI. For several days immediately subsequent to the occurrence of an MI, numerous episodes of VTxe2x80x94referred to as phase one episodesxe2x80x94typically occur. Eventually, the phase one VT episodes largely disappear. Several days or weeks later, though, additional episodes of VTxe2x80x94referred to as phase two episodesxe2x80x94typically begin to occur. It is the phase two episodes of VT that often transition to VF resulting in SCD of the patient. The risk of SCD is even greater if the patient also has an atrioventricular (AV) block, i.e. there is a partial or total interruption of the conduction of electrical impulses from the atria to the ventricles. AV block is common in patients who have had a MI.
Accordingly, it would be highly desirable to develop techniques for preventing VT from occurring, particularly phase two VT in a patients having an MI and, if VT does occur, for preventing the VT from transitioning to a VF. One technique employed in an attempt to prevent VT from occurring is overdrive pacing of the heart. With overdrive pacing, the heart is paced at a rate higher than is intrinsic pacing rate. If VT nevertheless occurs, one or more electrical cardioversion pulses are typically applied to the heart in an attempt to terminate the VT so that the VT does not transition to VF. If VF nevertheless occurs, one or more stronger electrical defibrillation pulses are typically applied to the heart in an attempt to terminate the VF thereby preventing SCD. Hence, for patients that have an MI, particularly a significant one, an implantable cardioverter-defibrillator (ICD) is often implanted into the patient. The ICD includes components for overdrive pacing the heart and for detecting VT or VF and for administering the appropriate therapy. However, the need to frequently overdrive pace the heart and to deliver cardioversion or defibrillation pulses can quickly deplete the battery power of the ICD requiring frequent replacement. Also, the therapies administered by the ICD, particularly the application of cardioversion pulses, may be extremely painful to the patient. Moreover, in some cases, the conventional therapy provided by the ICD is not sufficient to prevent or terminate VF and, accordingly, the patient succumbs to SCD.
Hence, it would also be highly desirable to develop new and more effective techniques for preventing VT or VF from occurring, particularly VT prevention techniques that do not require overdrive pacing and VF prevention techniques that do not require the administration of cardioversion or defibrillation shocks. A reliable prevention technique could greatly reduce need for overdrive pacing or shock therapy, thereby substantially extending the lifetime of the power supply of the ICD and eliminating the need for frequent surgical replacement of the battery supply. Most importantly, techniques for preventing the occurrence of VT or VF reduce the risk of SCD, and hence saves lives. It is to this end that the invention is primarily directed.
In accordance with one aspect of the invention, a method is provided for reducing the likelihood of the occurrence of an arrhythmia, such as VT or VF, in the heart of a patient. With the method, a neuro-stimulator is implanted in the patient and positioned for applying stimulation to the right stellate ganglion of the patient. Neuro-stimulation is then applied to the right stellate ganglion using the neuro-stimulator so as to stimulate nerve sprouting within portions of the myocardium supplied by nerves from the right stellate ganglion. It is believed that stimulation of nerve growth in the myocardium via the right stellate ganglion results in hyperinnervation of the sinus node and right ventricle of the heart which, in turn, reduces the occurrence of phase-2 VT and VF in the patient, particularly in patients having MI and AV block, and hence reduces the risk of SCD.
In an exemplary embodiment, the neuro-stimulator applies electrical stimulation to the right stellate ganglion. The electrical stimulation is applied at a sub-threshold level wherein the stimulation does not increase the heart rate or blood pressure of the patient. In other embodiments, the neuro-stimulator applies a neurotrophic vector such as Nerve Growth Factor (NGF), neurotrophic chemicals, neurotrophic substances, or neurotrophic hormones to the right stellate ganglion. In still other embodiments, the neuro-stimulator applies gene transfer techniques to cells of the right stellate ganglion to stimulate nerve growth.
In accordance with another aspect of the invention, a method is provided for use with a patient wherein neuro-stimulation is applied to the right stellate ganglion of the patient using a neuro-stimulator so as to stimulate nerve sprouting within portions of the myocardium supplied by nerves from the right stellate ganglion such that the risk of an arrhythmia occurring within the heart of the patient is reduced. Heart signals of the patient are then monitored to detect any arrhythmia that may nevertheless occur within the heart of the patient and, if an arrhythmia is detected, responsive therapy is applied.
In accordance with yet another aspect of the invention, a method is provided wherein a portion of the myocardium is selected wherein hyperinnervation is effective for reducing the occurrence of an arrhythmia in patients and then nerve growth is stimulated along a myocardial nerve pathway supplying nerves to the selected portion of the myocardium. In an exemplary embodiment, the portion of the myocardium selected for hyperinnervation is the sinus node and the right ventricle.
Aspects of the invention are applicable to treating patients with Brugada syndrome as well. Apparatus embodiments of the invention are also provided. Other objects, advantages and features of the invention will be apparent from the detailed descriptions which follow in combination with the attached drawings.